This invention relates to means for preventing over fusing, and more particularly to means of this type especially adapted for use with cartridge fuses having a notched terminal blade.
Electric cartridge fuses rated 100 Amperes and higher are provided with blade-type terminals adapted for insertion into a fuse holder comprising a spaced pair of fuse clips fastened to an insulating base. Conventionally, spring means are used to bias the jaws of each clip together to reliably contact and hold the terminal blade within the clip jaws. For one particular class of fuses having a relatively low range of rated currents, a notch is formed partially through the width of one of the flat terminal blades. Another particular class of fuse, having relatively higher rated current, is provided with flat terminal blades without notches.
The conventional fuse clip accepts the terminal blade of either class of cartridge fuse. A circuit having a relatively high current rating may have a fuse of lower rated current installed within its terminal clips to protect a load device having a current rating less than the circuit rating. Conversely, if a cartridge fuse having a current rating in excess of the circuit current rating is installed in a conventional fuse clip, an overcurrent fault hazard is present and the fuse will not provide current interruption and protection in the event of an overcurrent fault of magnitude sufficient to damage the circuit but less than the current rating of the fuse.
It is therefore desirable to provide means for use with a spring-bias terminal clip to facilitate installation of a notched terminal blade while preventing installation of a cartridge fuse having a higher current rating and an unnotched terminal blade. The rejection means must be capable of being field installed in a relatively simple manner in a fuse clip, preferably without requiring the use of tools, and must be extremely difficult to remove once installed to prevent subsequent unauthorized removal.